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A. A. DITTMAR. GALVANOMETEB.

(Application filed Aug. 27, 1898.) (No Model.)

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U ITED STATES PATENT OFFICE.

ALLEN A. DITTMAR, JERSEY CITY, NEl/V JERSEY, ASSIGNOR TO HARRY T.JOHNSON, OF SAME PLACE.

GALVANOM ETER.

SPECIFICATION forming part of Letters PatentNo. 619,679, dated February14, 1899. Application filed August 2'7, 1898. Serial No. 689,633. (Nomodel.)

To alt whom it may concern:

Be it known that I, ALLEN A. DITTMAR, a citizen of the United States,and a resident of Jersey City, in the county of Hudson and State of NewJersey, have invented acertain new and useful Galvanometer, of which thefollowing is a specification.

This invention relates to an improvement in rotary-disk armaturesespecially designed for use in electromagnetic instruments-such, forinstance, as galvanometers.

The main object of the invention is to construct an armature for agalvanometer or other indicator which shall be accurately balanced andwhich shall have an extended de gree of rotation, so as to provide forconstructin g an indicating instrument on a small scale and still enablethe graduations of its scale to be made legible.

With this object in view the invention consists in the construction,arrangement, and combination of parts hereinafter fully described, andset forth in the claims.

In the accompanying drawings, which form a part of this specification,Figure 1 represents a pocket-galvanometer embodying the invention. Fig.2 represents a vertical transverse section through the same, taken onthe line 2 2 of Fig. 1. Fig. 3 is a face view of the rotary armaturedrawn on an enlarged scale. Fig. 4is a diametrical section thereof,taken on line 4 i, Fig. 3.

In describing this invention reference will be had to its embodiment ina pocket-galvanometer.

The case of the galvanometer represented at A may be and preferably is awatchcase. This may have an open face, as shown, or may be of thehunting-case pattern, if desired.

The electromagnet of the galvanometer is indicated at B and has itsupper pole-piece divided, as indicated at (J. The recurved pole-piece Dis attached to the lower end of the magnets core and serves as thesecond pole-piece of the magnet. This pole-piece also serves to supportthe magnet and other mechanism of the galvanometer and is magneticallyinsulated from the case by the interposition of the copper plate E.

Upon the pole-piece D is journaled the armature F, which is in disk formand extends between the portions of the divided pole-piece C, asindicated. This is preferably made very thin and light, so much so thatan ordinary hair-spring, as indicated at G, is sufficient to return itto the initial or zero point, where it is stopped by engagement with thepole-piece O of a suitable pin or projection H, carried by the disk.Upon the arbor carrying the armature there is mounted the hand orpointer I, which travels over a scale J.

The binding-posts of the instrument are indicated at K, from one ofwhich current is led to'the magnet through the case and the conductor L,while the other is insulated from the case and connected to the magnetby the conductor M.

To construct a successfully-operating galvanometer on so small a scale,it is necessary that the armature or movable part thereof be as light inconstruction as possible and that its moments of inertia shall be asnearly as possible equalized. To this end the armature F is made in theform of a circular disk and composed of a spiral or snail, of magneticma- 7 5 terial, as iron, extending about the periphery thereof andterminating at the center, the convolutions being separated bynon-magnetic material, such as brass, which is indicated at N. As willbe noted, the spiral or snail, of magnetic material, begins, as at O, ina narrow point and gradually widens until it reaches the stop H, whichis but a short distance from the point 0. The non-magnetic material Nbreaks through to the periphery between the points H and O. The normalposition of the disk brings the point 0 just within the gap between thedivisions of the pole-piece. The disk is preferably made by stamping outthe iron snail and the brass 9o.

snail and then inserting one within the other and brazing them together,thereby making a disk of uniform surface and extent and of equalmoments. Brass is chosen as the non- Other non-magnetic material may beused in the place of brass, if desired, provided the resultant disk willbe balanced.

In the operation of the instrument as soon as the current is permittedto pass through the magnet 13 the disk begins to rotate, because of theattraction of the pole-piece O for the greater mass of the snail, andthis continues until that tension is placed upon the spring Gproportionate to the amount of current to be measured, which amount willbe indicated by the pointer. Then upon cutting ofi the current from thegalvanometer the spring will turn the disk to its normal position, withthe stop H resting against the pole of the magnet, at which time thecurrent will be at zero.

The galvanometer constructed on this plan may be easily calibrated andabsolute accuracy secured in its operation.

While the armature, as shown, ispolarized by direct connection with thepole-piece D,

and thereby of opposite polarity to the divided pole of the magnet, itis obvious that said armature may be given the desired polarity byothermeans.

The invention claimed is-- 1. I11 an electromagnetic device, a compounddisk of magnetic and non-magnetic balancing metal, the magnetic portionof the disk being in the spiral or snail form while the non-magneticmaterial fills the remainder of the area comprised within the peripheryof the disk so as to produce a disk which is balanced in all positions.

2. In an electromagnetic indicating device, the combination with anelectromagnet having a divided pole-piece, of a convolute or snailshaped armature magnetically -connected to the opposite poleof themagnet and movable between the divisions of the divided pole-piece bywhich it is attracted continuously in the same. direction, or inopposition to the retractor, through its whole range of movement,substantially as set forth.

3. The combination with the casing, of the recurved pole-piece mountedtl1erein,the compound balanced disk armature constructed substantiallyas described journaled in the upper portion of said pole-piece andmagnetically connected therewith, the electromagnet mounted on the lowerend of the recurved pole-piece and having its other pole-piece dividedand the divisions thereof placed on either side of said armature, aspring opposing the attractive action of the divided polepiece in allpositions of the armature, and a pointer carried by thearmature,substantially as and for the purpose set forth.

4. A disk "armature consisting of an iron spiral or snail forming theperiphery of the disk and terminating at the center thereof, and aspiral of non-magneticmaterial as N, interposed between theconvolutionsof the iron spiral, the two spirals being brazed together to form acompleteandvrigid disk, substantially as shown and described.

5. The combination with the balanced convolute or snail-shapedarmature-disk of one polarity and its retractor, of amagnet having adivided pole-piece of opposite polarity so placed that the disk shallrevolve-between the divisions by the attraction thereof exerted uponconvolutions of the diskat all positions thereof in a direction tooppose the influence of the retraetor.

Signed at New York, in the county-of New York and State of New York,this 26th day of August, A. D. 1898.

ALLEN A. DITTMAR.

Witnesses:

WM. H. OAPEL, DELBERT II. DECKER.

